Note (return) — Chapter IX

The Sophists, who belonged to no particular school, laid hold on the elements of skepticism contained in both the pre-Socratic schools of philosophy, and they declared that "the σοφία" was not only unattainable, but that no relative degree of it was possible for the human faculties. 468 Protagoras of Abdera accepted the doctrine of Heraclitus, that thought is identical with sensation, and limited by it; he therefore declared that there is no criterion of truth, and Man is the measure of all things. 469 Sextus Empiricus gives the psychological opinions of Protagoras with remarkable explicitness. "Matter is in a perpetual flux, whilst it undergoes augmentations and losses; the senses also are modified according to the age and disposition of the body. He said, also, that the reason of all phenomena resides in matter as substrata, so that matter, in itself, might be whatever it appeared to each. But men have different perceptions at different periods, according to the changes in the things perceived.... Man is, therefore, the criterion of that which exists; all that is perceived by him exists; that which is perceived by no man does not exist." 470 These conclusions were rigidly and fearlessly applied to ethics and political science. If there is no Eternal Truth, there can be no Immutable Right. The distinction of right and wrong is solely a matter of human opinion and conventional usage. 471 "That which appears just and honorable to each city, is so for that city, so long as the opinion prevails." 472